1. Field of the Invention
The present invention relates to a probe system comprising a plurality of probe units for measuring the electric characteristics of an object to be measured, e.g., a semiconductor wafer.
2. Description of the Related Art
In a semiconductor device manufacturing process, IC chips are completed in a wafer, the wafer is cut into chips, and thereafter the chips are packaged. The respective chips in the wafer are subjected to an electric measurement called a probe test by a probe apparatus before packaging in order to eliminate a defective chip.
A conventional probe apparatus has a box, a measurement stage provided at the central portion in the box and movable in the X, Z, and .theta. directions, a probe card provided above the measurement stage and having a plurality of probes, and a wafer transfer chamber provided next to the measurement stage in the box. For example, upper and lower wafer carriers and a transfer mechanism for transferring wafers between the wafer carriers and the measurement stage are provided in the wafer transfer chamber.
In this probe apparatus, four wafer carriers each storing, for example, 25 wafers are arranged in the wafer transfer chamber. One wafer is taken out from each carrier and placed on the measurement stage by the transfer mechanism. Subsequently, the electrode pads of the IC chips of this wafer are electrically connected to a test head through the probes to perform measurement. When the measurement is completed, this wafer is returned to the wafer carrier by the transfer mechanism. When measurement of all the wafers is completed, these four wafer carriers are replaced by four new wafer carriers by an operator.
In this manner, the probe apparatus performs measurement in units of wafers. Since a time required for measuring one wafer sometimes exceeds one hour, a large number of, for example, 100 or more probe apparatus are often installed in a clean room in order to increase the throughput.
The conventional probe apparatus has, however, the wafer transfer chamber in addition to members required for measurement, such as the measurement stage and the probe card, as described above. Since four wafer cassettes are housed in the wafer transfer chamber each time in order to improve the operation efficiency, the space occupied by the transfer chamber is rather large. Recently, as the diameter of the wafer is being increased from 6 inches to 8 inches, the transfer mechanism becomes complicated, leading to an increase in size of the probe apparatus. When a large number of probe apparatus are installed, as described above, a large proportion of the space of the expensive clean room is occupied by only the probe apparatus.
When a large number of probe apparatus are arranged in this manner and wafers are conveyed to the respective probe apparatus, particles are produced and attach to the wafers during conveyance.
Furthermore, when the large number of probe apparatus are arranged in the clean room, it is difficult to perform efficient electrical measurement of wafers using all the probe apparatus.